This invention relates to a composite material which comprises an aluminum cast matrix and a metal cladding material, and method for producing the same. More particularly, the invention relates to a composite material comprised of an aluminum cast matrix and a ferrous cladding material and a method for producing the same, in which a powder of iron or its alloy, or copper or its alloy, or mixture thereof is joined to the surface if a ferrous cladding material by sintering and aluminum or its alloy is cast on the sintered surface.
A composite material made of an aluminum or aluminum alloy matrix and a ferrous metal bonded to the matrix, is generally used, for example, for making cylinders of internal combustion engines and brake drums in which aluminum or its alloy alone can not withstand the severe conditions and ferrous metal alone provides its problems of its weight and cost. As the method for joining a different kind of metal to the matrix of aluminum or its alloy, there are known in the prior art a method in which the surfaces to be joined are made jagged and they are mechanically joined together, the Al-Fin process which utilizes a chemically joining force, the transplanting process which utilizes molten jet layers, and so forth.
In the Al-Fin process, however, the pretreatment of the ferrous material is complicated. In addition, the casting must be done while the aluminum is molten or with the melting of aluminum since molten aluminum must be used. Thus, the production process becomes very complicated and it is difficult to obtain stable quality products. Further, an aluminum-iron alloy is liable to be formed on the joined surfaces and this aluminum-iron alloy is brittle so that a sufficient bonding strength can not be maintained under some conditions and the product can not be used under conditions in which a large thermal load and impacts are applied therein.
In the transplanting process, a large number of steps are required since molten jet layers are utilized. In addition, iron oxide is intermixed during the step of applying the molten jets so that the machining after such step becomes quite difficult. Further, the thermal conductivity of iron oxide is very low so that, when the products are used as parts which receive a large thermal load, a satisfactory result can not be expected. These have been the problems remaining to be solved in the conventional art.
Still further, in the method utilizing the mechanical joining of jagged surfaces, the bonding strength is not satisfactory when simple rough surfaces are mechanically joined together. In order to improve the joining strength, therefore, several methods are proposed, for example, a method of pressing and enlarging the projections on the joining surface into a mushroom-shape, or a method of plating the joining surfaces with zinc so as to effect diffision bonding, or a method utilizing both the above methods. In these methos, however, the deformation of the projections is difficult and when plating is employed, the difficulties in process control and environmental pollution become problems. Furthermore, since the projections formed on the surface to be joined become lage in such methods, they can not be employed for joining relatively thin ferrous cladding materials. On the other hand, if thicker materials are used, the weights of the parts become large so that it is not suitable for making lightweight parts.